【作者】 覃昕慧；

【导师】 陈刚； 李国栋；

【作者基本信息】 西安理工大学 ， 水力学及河流动力学， 2010， 硕士

【摘要】 随着水利水电工程建设的发展,泄水建筑物的泄流量越来越大,单宽流量进一步增加,与之相关的脉动、空化空蚀等高速水流问题日益突出。向高速水流中掺气,是减免建筑物发生空蚀破坏的主要工程措施。因此,开展溢洪道水力特性,特别是掺气水流特性的研究对泄水建筑物的安全运行具有重要的现实意义。鉴于数值计算具有易操作、低成本和短周期等优越性,在建筑物的选型和优化设计工作中,数值模拟方法能发挥较大的作用甚至部分代替试验,缩短周期。但是由于涉及掺气的理论还很不成熟,对其进行数值模拟还有许多研究工作需要去做。本文对巴贡水利工程中长溢洪道整体三维流场进行了数值模拟计算,以期深入了解其水力特性,为溢洪道的合理设计提供依据。采用多相流模型,对掺气坎处的掺气水流进行了模拟,通过对不同气泡特征直径,不同相间作用力模型计算结果的对比分析,探索改善掺气水流预测水平的途径,。本文选用标准κ-ε紊流模型,有限体积法离散控制方程,VOF方法模拟自由表面,对不规则边界采用非结构网格进行处理。通过对该工程溢洪道紊动流场进行的三维数值模拟,得到了泄流量,速度场、压力场、水面线等的分布规律。数值模拟和试验结果的对比分析,两者吻合较好,表明模拟结果能满足工程需要。对于掺气坎附近水流及掺气的模拟,本文采用双流体理论的欧拉模型,考虑水气间的相互作用,并以某个特征直径气泡代替气相对其进行模拟。计算结果表明,采用欧拉模型能较好的模拟出通气孔处的风速和通气量,不同的特征直径气泡对通气量的影响较为明显,但总体上来说,模拟值较实测值偏大。跌坎下游的掺气浓度无论实验数据和模拟结果,均显示水体中心部位掺气浓度沿程衰减,但模拟值的衰减率明显小于实测值,空腔负压较实测值偏大,导致模拟得到的掺气空腔不完整。在考虑充分通气的情况下,对比两种不同相间作用力模型对下游掺气浓度的影响,采用对称模型时特征气泡直径对水面气泡上浮影响较大,但掺气沿程衰减不明显的现象依然没有得到很好的改善。由于紊动、水气两相流以及自由面问题的复杂性,两相流机理还处在发展阶段,并且由于气泡大小分布和变化规律尚不明确,在掺气模拟方面依然还有很多问题有待进一步探索。更多还原

【Abstract】 With the development of hydropower engineering industry, the discharge of outlet structure is getting greater and greater,unit discharge is further increasing and problems brought by high velocity flow such as pulsating movement,cavitation and erosion become more prominent day by day. The main engineering measure to prevent cavitation damage of the stucture is to add gas into high velocity flow.Therefore,study on the hydraulic characteristics of spillway,especially on aerated flow,becomes more and more important for safe operation of outlet structure.As numerical simulation has the advantages of handleability, low cost and short cycle and so on,it can play a larger role and even replace apart of test in the construction selection and optimization,the period can be shorted.Because the theory of aerification is not very mature,there is mass of numerical simulation research ahout it to be done.In order to understand the hydraulic characteristics of spillway and provide basis for rational design,the numerical simulation of flow field of spillway in BaGong Project is done in this paper. The simulation of aerated flow at aerator is done with multiphase model, A new avenues to better improve the forecast level of aerated flow will be explored by comparisons of the caculation results in the case of characteristic diameter of different bubbles and different forces between phases.Standardκ-εmodel combining with finite volume method are applied to this paper,free surface was trated with VOF method and irregular boundaries were dealed with unstructured grid.Compared with the data of model test of engineering project, a three-dimensional numerical simulation of turbulence of the spillway in this project was done,the discharge, velocity field, pressure field and water surface profile were all obtained. The comparison analysis shows that numerical simulation was in good accordance with experimental results,which satisfied the engineering requirements.In order to exactly study the flow near the aerator, the two-fluid of Eulerian Model is used in this paper.Considering the interaction between gas and liquid.the simulaiton is done with a acharacteristic diameter bubble instead of gas.The results show that the ventilation volume and wind speed by the vent are obtained with Euler model, the different characteristics diameter of bubble has a notable impact on ventilation volume,yet on the whole,the values of simulation are a little greater than the experimental ones. The experimental datas and simulation results show that,air concentration of simulation results is smaller than experiment and negative pressure and cavity is greater than it which lead to the cavity is incomplete.In view of the condiotn of sufficient aeration,the impacts of two different interphase forces model on air concentration of downstream are compared,the diameter of characteristic bubble has a great effect on bubble floating on the water surface with symmetric model in compution,but the phenomenon that on-way attenuation of aerification is inapparent has not been improved better.Because of the complexity of turbulent flow, water-air two-phase flow and free surface, two-phase flow mechanism is still in development stage, because the bubble size and the variation is not clear, the numerical simulation of aerated flow still has many questions to be further explore更多还原